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Abstract:

A floating platform for wind energy extraction, comprising a structure
(S) which is the support for the assembly (P) made up of a wind turbine
tower (3), a nacelle (2) and its corresponding rotor blades (1), whereby
the support structure (S) is formed by an upper structure (4) which joins
the assembly (P) to the floating tank (5), which is, in turn, joined by
means of a lower structure (7) to the ballast tank (8), and whereby said
ballast tank (8) is configured to control the assembly's centre of
gravity and adjust the flotation line by the distribution of mass.

Claims:

1. A floating platform for the extraction of wind energy, comprising a
structure (S) which is the support for assembly (P) made up of a wind
turbine tower (3), a nacelle (2) and its corresponding rotor blades (1)
characterised in that the support structure (S) comprises an upper
structure (4) which joins assembly (P) to the float tank (5), which, in
turn, is joined by means of a lower structure (7) to the ballast tank
(8), and whereby said ballast tank (8) and said lower structure (7) are
configured to control the unit's centre of gravity and adjust the line of
flotation by means of the distribution of mass.

2. A floating platform in accordance with claim 1, whereby the float tank
(5) comprises a cylinder (5a) joined to a tapered ferrule (5b) which
joins it to the upper structure (4) and to another tapered ferrule (5c)
which joins it to the lower structure (7).

3. A floating platform in accordance with claim 1, whereby the lower
structure (7) is made from steel plate and is tapered, with a greater
diameter at its connection with the float tank (5) than at its connection
with the ballast tank (8).

4. A floating platform in accordance with claim 1 whereby the ballast
tank (8) is hollow and can be filled and emptied in a controlled fashion
in numerous watertight compartments.

Description:

[0001] The main object of the present invention refers to a floating
platform for the generation of electrical energy from wind. This platform
can be applied in the field of renewable energies, specifically in the
area of so-called off-shore wind energy, that is, at sea and far from the
coast.

PRIOR ART

[0002] Marine wind energy projects have higher installation, operation and
maintenance costs than those onshore. The foundations for marine wind
turbine towers account for a major part of this initial outlay, which
increases with depth, with the result that, currently, at a depth of 50
metres or more, it is economically favourable to use floating platforms.

[0003] It is increasingly difficult to find suitable sites for the
installation of onshore wind turbines. Consequently, the international
tendency is for marine wind farms to be installed in the national waters
of each country. However, in many places the water reaches a depth of 50
metres a few kilometres from the shore. As a result, to install a
significant number of marine turbines, we need technical solutions
allowing the installation of wind farms in seas with depths of greater
than 50 metres. The most promising idea from the point of view of
efficiency is the development of a floating structure that supports a
wind turbine. Marine wind energy resources are more abundant and
continuous than those on shore, which is why it is a great source of
renewable energy which has yet to be exploited on a large scale in these
types of sites.

[0004] The floating platform which is the object of this invention
consists in a structure capable of supporting the weight of the rotor,
turbine and wind turbine tower by means of a float, almost irrespective
of the depth of the sea. Although there is currently no similar structure
in operation, there are precedents in this field of application.

[0005] Thus, patents WO2006132539 and U.S.20070228739 describe two
structures whose angles of heel are very high, due to the fact that they
do not contemplate the generation of an adequate righting torque. This
impedes the proper exploitation of wind energy by the wind turbine,
giving very low yields which can make both systems economically unviable.
Moreover, in the case of patent WO2006132539, part of the structure is
made from concrete and, given the necessary volume in an actual
construction, it could make the building and transport difficult, given
its weight and considering that the difference in cost with certain types
of steel is very low. In addition, in the case of patent U.S.20070228739,
wind energy is used to power an internal generation process of another
type of energy and not for its extraction to the general supply network.

[0006] For its part, patent WO03004869 defines a single tank below sea
level which acts as a float and ballast at the same time. If a structure
of this type wishes to limit its angle of heel, it would need such a
large volume that it would be technically and economically unviable to
build. Limitation of said angle of heel and, consequently, its stability,
must be achieved by means of a restoring torque due to the
weight/floatability forces torque and the separation of said forces. In
the absence of a stability system made up of differentiated structures
for the floatability of the system, such as a floating tank and a ballast
tank, it is not possible to obtain great yields, based on smaller
dimensions and lower costs for similar generated power. Both structures
need to be separated by means of a lower structure, thereby raising the
distance between the restored forces and requiring less force for the
same restoring torque.

[0007] Lastly, patent U.S.20060165493 describes a system based on three
floating supports, with the resulting proportional rise in costs.

DESCRIPTION OF THE INVENTION

[0008] The floating platform that is the object of the invention is made
up of a semi-submerged structure which is anchored to the sea bed by
means of a mooring kit. The whole system generates a righting torque
thanks to an adequate distribution of weight and volume that guarantees
the working of the wind turbine with angles of heel below 10°. The
entire structure and its purpose is in itself a novelty, given that no
similar structure is currently in operation. This invention solves the
problems that arise in seas with depths above 50 m, where it is
economically unviable to install wind farms.

[0009] The system's stability is attained thanks to the restoring torque
due to the weight-floatability forces torque, and the separation of said
forces. The present invention proposes, as a main difference, the
creation of a stability system made up of differentiated structures for
the floatability of the system--floating tank--and ballasting of the
same--ballast tank--, located in the upper part in the case of the float
and in the lower part of the stability system for the ballast tank. Both
structures are separated by means of the inferior structure, thus
increasing the distance between the restoring forces and requiring less
force for the same restoring torque. This set up implies higher yields
than those proclaimed in the documents reflecting the status of the
technique, requiring smaller dimensions and, consequently, lower costs
for an equivalent generated power.

[0010] The system which is the object of this invention is made up of an
upper structure that joins the wind turbine tower to a float tank. The
upper structure is made of steel and is joined to the wind turbine tower
and the float by means of bolting flanges. Its purpose is to ensure at
all times that the tower is above the water and the float submerged. This
design ensures the floating structure is independent of the tower
required for each wind turbine. In addition, the weights and volumes
calculated ensure that the float is submerged, which is an indispensable
condition to ensure inclinations of below 10° and to ensure the
proper working of the wind turbine.

[0011] The connection between the float tank and the ballast tank is made
by means of a central structure. This element is made from steel plate
and is tapered with a greater diameter at the connection with the float
than at the connection with the ballast. This part ensures the
transmission of forces due to righting torque which stabilises the system
as well as providing a considerable proportion of the flotation.
Internally, it has a system which allows flooding and partial emptying
for the necessary adjustment of the flotation line. This flotation line
adjustment system is a major innovation for the viability of the assembly
of the entire structure.

[0012] The ballast tank is a container in charge of storing ballast (which
can be sand) in such a way that it allows the centre of gravity of the
entire structure to be lowered. This container is metallic and has
several compartments so that it can be filled in a controlled fashion.
This system of adding and removing ballast allows the assembly and
installation of the entire system and is a novelty in structures with
these characteristics.

[0013] It is tethered to the sea bed by means of three moorings which have
an initial preload with an aim to reducing the shifts in the entire
system when it acts on the force of the waves or wind. The moorings are
tethered to the sea bed by means of ballasts or anchors depending on the
type of seabed and the depth of the installation site. Given the
importance of the anchorage system as an integral part of the balance of
weights and volumes of the whole system, and given its importance in
overall stability, this system is novel for its specific characteristics.

[0014] The advantages afforded by the system described herein lie in the
fact that the restoring moment of the support for a given size of float
is maximised. The aim is to attain the maximum possible separation
between the elements that provoke flotation and the elements that
stabilise, thus rising the system's restoring torque.

[0015] The range of use of the system is very broad, from depths of 50
metres to depths of several thousand metres. The invention described
manages to increase the range of use to zones with depths of less than
100 metres, which is why supports capable of functioning in depths of up
to 50 metres can be obtained, making lightweight, modular supports that
facilitate logistics and reduce costs.

[0016] The variation in the thrusts on the floating platform due to
variations in the sea level (such as waves, tides and others) is
drastically diminished, as the greater volume of flotation is
concentrated in the float and this is far from the flotation line.

[0017] The structure has greater transparency to waves and the currents in
the areas where volume is not strictly necessary, as, for example, in the
lower structure (the area between the float and the ballast). This
contributes to a reduction in the floating platform movements and,
consequently, an improvement in its performance with respect to other
solutions.

[0018] The large diameter of the float tank with respect to other parts of
the structure is used as a point of connection of the moorings, and
affords a considerable restoring torque for the rotation of the floating
platform on its own axis.

BRIEF DESCRIPTION OF THE FIGURES

[0019] Below is a very brief description of the drawings which help to
understand the invention and which are expressly related with an
embodiment of said invention which is presented as a non-limiting example
of the same.

[0020]FIG. 1 shows a front view of the floating structure capable of
supporting a wind turbine which is the reason for the invention.

PREFERRED EMBODIMENT OF THE INVENTION

[0021] As can be seen in FIG. 1, the floating platform for the extraction
of wind energy proposed herein is made up of an upper structure (4) which
joins the wind turbine tower (3) to the float tank (5). The upper
structure (4) is made of steel and is joined to the wind turbine tower
(3) and to the float (5) by means of bolting flanges. Its purpose is to
ensure at all times that the wind turbine tower (3) is above water and
the float (5) is submerged.

[0022] The currents exert drag force on the structure which depends on the
size of the current and the cross-sectional area exposed to the same. On
the other hand, the structure is subjected to the action of the waves
which again exert drag force and afford the system oscillatory movements.
These forces are greater on the surface and diminish as one goes deeper
and are practically null on the seabed. With an aim to reducing the
action of the currents and waves on the structure, an upper section (4)
is proposed to act as an air-water interface and has a cross-section area
equal to or smaller than that of a cylinder of the tower's base diameter.
The forces that the currents and waves may exert on the structure are
thus minimised and consequently its movements. Possible alternatives for
the upper structure (4) are cylinder-shaped or tapered solutions with a
small diameter or solutions based on lattice tubes that have an even
smaller cross-section area. This upper structure rises approximately 15 m
above the surface of the water and extends 20 m under the water, thus
covering the area in which the force of the current and waves is
greatest. On the other hand, the up and down movement of the floating
platform is related to the section or area of this upper structure on the
flotation line. A smaller area in this section provokes little change in
the system's floatability on the passing of the wave; with the result
that the platform's up and down movement is reduced.

[0023] The float tank (5) is made up of a cylinder (5a) joined to two
tapered ferrules (5b, 5c) which enable the rigid connection between this
element and the upper structure (4) and the lower structure (7). The
greatest percentage of the system's flotation is concentrated in the
float tank (5). The float (5) is made up of a steel hull internally
reinforced by bulkheads in both directions. The connection with the upper
(4) and lower (7) structures is made by means of bolting flanges.

[0024] The float tank (5) is in charge of affording the system
floatability. Said float (5) is made up of a watertight structure full of
air, joined, above, to the upper structure (4) and, below, to the lower
structure (7). In addition, it has a system of forces which allows it to
transmit the mechanical solicitations of the upper structure to the lower
structure, with the whole assembly acting as a solid rigid body. The
separation between the float tank (5) and the ballast tank (8), that is,
the length of the lower structure (7) is fundamental to increase the
restoring torque of the floating platform and its performance,
performance being understood as the weight of the structure in relation
to the restoring torque that it affords. In other words, it can be said
that, once a restoring torque has been established, the volume of float
required for the proposed platform is less the greater the length of the
lower structure, performing far better than other solutions.

[0025] The float tank (5) and the ballast tank (8) are joined by means of
a lower structure (7). This element is made of steel plate and is tapered
in shape, with a greater diameter at the connection with the float (5)
than at the connection with the ballast (8). This part ensures the
transmission of forces due to the righting torque which stabilises the
system as well as contributing considerable flotation. Internally, it has
a system which allows flooding and partial emptying for the necessary
adjustment of the flotation line.

[0026] The ballast tank (8) is a container in charge of storing ballast
made up of a liquid (water) mixed with a solid material (which can be
sand) in such a way that it allows the centre of gravity of the entire
structure to be lowered. This container is metallic and has several
compartments so that it can be filled in a controlled fashion.

[0027] With an aim to reducing the action of the currents and waves on the
lower structure, cylindrical, tapered, solutions are proposed or based on
lattice tubes or mixed solutions, that is, an upper section (4) based on
lattice tubes and a lower section (7) based on cylinder or stepped
tapers. The object is to reduce, to the greatest extent possible, the
surface area exposed to the action of currents and waves. The forces that
the currents and waves may exert on the structure are thus minimised and,
consequently, its movements and, therefore, the platform's performance is
enhanced. This lower structure (7), as has been pointed out, is in charge
of separating the float tank from the ballast area, whereby the distance
between the restoring forces is increased and, consequently, greater
restoring torques are achieved for a given floatability. This implies
smaller and more lightweight structures, if the restoring torque is
fixed. The performance of the system, measured as restoring torque
against structure weight, is considerably heightened. The use of this
element implies a substantial difference with respect to the solutions
put forward by previous patents, as the improved behaviour of the
platform added to the enhanced performance, implies smaller structures
and, consequently, lower costs for wind turbines of similar size.

[0028] Anchorage to the sea bed is ensured by means of three anchorage
lines (6) which have an initial preload with an aim to reduce the shifts
in the entire system when it acts on the force of the waves or wind. The
moorings are tethered to the sea bed by means of ballasts or anchors (9)
depending on the type of seabed and the depth of the installation site.